Feature Extraction. As shown in Fig. REF , we employ 3-layer EdgeConv [1]} to embed \(\mathcal {P}\)  into a high-dimensional feature space, producing hierarchical features, \(\lbrace \mathbf {c}_i^{(l)}\in \mathbb {R}^{d_1}\rbrace _{i=1}^{N}\) , \(l=1,2,3\) , which are concatenated as the point-wise features of \(\mathcal {P}\) .
